Any of 12 species of solitary marsh birds (family Ardeidae), related to herons but having a shorter neck and a stouter body.
Most bitterns bear a camouflage pattern (streaks of variegated brown and buff) that enables them to hide by standing upright with bill pointed upward, imitating the reeds and grasses of their habitat. They feed on fish, frogs, crayfish, and other small swamp and marsh animals, which they spear with their sharp-pointed bills. Bitterns are found almost worldwide. The largest species grow to 30 in. (75 cm), the smallest to about 12–16 in. (30–40 cm).